Robot uses its tail to land on its feet, just like a cat

An engineering team has published a paper revealing that by
giving a robot
the right tail, it can always land on its feet -- just like a cat.

The University of Pennsylvania's Kod*lab appears to have
found a way to gracefully circumvent a robot's embarrassing
tendency to scrabble helplessly at the air, like a bug on its back,
when it lands awkwardly. In experiments sending the six-legged X-RHex
Lite running off a 62cm-high cliff edge and then into a nosedive
from eight times its standing height, the team discovered the robot
always righted itself mid-air in time for impact using the "dynamic
locomotion" (tail swinging) employed by some in the animal
kingdom.

"By swinging their tails, geckos can self-right in less than a
body length after a fall, or reorient through zero net angular
momentum manoeuvres," explains the
paper, published in the Proceedings of the International
Conference on Climbing and Walking Robots, July 2012.

"The eﬀectiveness of this mechanism inspired Tailbot, a robot
with an active tail which enabled disturbance regulation and other
dynamic behaviours, including air-righting and traversing rough
terrain. The stabilising function of tails appears to operate
eﬀectively over a wide range of size scales in natural systems,
from one gram geckos to 10 kg lemurs and possibly beyond."

The team decided to see if the same could be said of robots of
different sizes, so fit the extra appendage to a model 60 times
bigger than the tiny Talibot (a toy car device with a lizard-like tail attached). In keeping with the Talibot's
design, the brass tail weighed about a tenth of the robot's body
mass and was attached to a carbon fibre tube the length of its
body. Airborne self-righting was achieved by the 8.1kg
hexapedal X-RHex Lite by ensuring that the "power density of the
tail's actuator" increased with size "in order to achieve the same
manoeuvre in the same relative time". This was made possible by
using a "point mass" tail -- a tail that carries the bulk of its
mass at the tip. Using its inertial navigation sensors, the
robot detects its rotation or the upcoming cliff edge and activates
the tail to realign the body pitch.

The paper concludes that adding a tail is an ideal solution to
helping create autonomous robots, since mechanisms that are already
developed can simply have the appropriately-sized appendage
attached, rather than undergo a total structure amendment to
achieve the same effect.